286. Walls and Gates

from collections import deque

class Solution(object):
    def neighbors(self, rooms, x, y):
        dx = [0,0,-1,1]
        dy = [-1,1,0,0]

        q = deque()
        q.append((x,y))
        step = 1

        while q:
            num = len(q)
            for i in range(0, num):
                xx, yy = q.popleft()
                for i in range(4):
                    rx, ry = xx + dx[i], yy + dy[i]
                    if rx < 0 or ry < 0 or rx > len(rooms)-1 or ry > len(rooms[0])-1:
                        continue
                    if rooms[rx][ry] > 0 and rooms[rx][ry] > step:
                        rooms[rx][ry] = step
                        q.append((rx, ry))

            step += 1


    def wallsAndGates(self, rooms):
        """
        :type rooms: List[List[int]]
        :rtype: void Do not return anything, modify rooms in-place instead.
        """
        if not rooms or not rooms[0]:
            return

        for i in range(0, len(rooms)):
            for j in range(0, len(rooms[0])):
                if rooms[i][j] == 0:
                    self.neighbors(rooms, i, j)